In general, when a subscriber having a mobile station (MS) or terminal located within a first PLMN wishes to contact another subscriber having a mobile station or terminal located in a different PLMN, the first mentioned subscriber's MS must transmit to its serving mobile switching centre (MSC) operating capabilities, such as, a codec or a list of codecs on which it can transmit information or messages. Negotiation must then be initiated, typically, over a fixed switched network, such as PSTN, or ISDN, IP or ATM with the other mobile station or terminal. Once operating capabilities are negotiated between the two mobile stations then the call may proceed using those capabilities. All of this negotiation requires a lot of signalling to take part between the originating mobile station and its serving MSC each time a call needs to be established.
As mobile networks are becoming more and more advanced and requiring the transmission of greater amounts of data between nodes of the network or across other networks such as a PSTN or ISDN fixed network, this creates a burdensome task for nodes within the network to process all the data. Furthermore, the signalling process takes place relatively slowly. It would therefore be desirable to remove extra data, where possible, especially between an MS and its serving MSC, in order to increase the speed of signalling and reduce the signalling load between the MS and MSC, especially for example, at call set-up. By reducing the amount of signalling data that needs to be transmitted between an originating mobile station and its serving MSC, the network resources could be more efficiently used.
In one particular arrangement, developed by the present applicant, a Bearer Independent Call Control (BICC) protocol is used for negotiating operating capabilities, and in particular codec negotiation. The BICC protocol is particularly suitable for third generation mobile networks, such as UMTS, wherein non-TDM transport technologies are used. However, the proposed BICC codec negotiation is not fully optimised for mobile environments. In particular, it is not optimised for fast selection of operating capabilities for mobile terminated calls when, for efficiency reasons, transcoders are placed in the edge of the core network at the GMSC.
The present invention seeks to overcome or substantially ameliorate at least one of the disadvantages of the prior art.